As computer technology has advanced the number of computers being used, as well as the tasks these computers are being used to perform, has increased. One significant area of advancement has been with portable computers, resulting in increasingly powerful computers being manufactured in small, easily mobile packages. Such mobility, in turn, has led to an increase in the desire for the availability of peripheral devices, such as printers, to computer users in non-traditional locations (that is, in locations other than at work or home). An example of such a non-traditional location is a hotel room—placement of a printer in a user's hotel room makes the printer readily available to the user when staying in that hotel room.
Unfortunately, in order for businesses to be willing to place peripheral devices in public places such as hotel rooms, these businesses need to be able to guard against theft of not only the devices themselves but also components of the devices. For example, printers typically include print substance stored in one or more cartridges (e.g., ink cartridges or toner cartridges) or refillable reservoirs. Because the print substance is used up during the normal process of printing, it is common for the printers to be designed so that the cartridges are easily replaceable or reservoirs easily refillable. However, by making such replacement or refilling easy, the print substance is also subject to easy theft. For example, an unscrupulous user could bring his or her own depleted ink cartridge to a hotel room and swap it for a near-full cartridge in the printer of that room.
One solution to guard against such theft is constant surveillance of the device (e.g., by video camera). However, such surveillance is costly and in many situations would be viewed by users as an unreasonable intrusion of their privacy. Another solution is to physically restrict access to the replaceable cartridges (e.g., by using a lock to which only appropriate staff have a key). However, this too has problems as it makes replacement of cartridges (or refilling of reservoirs) more cumbersome and also increases the cost of the printer by requiring either additional mechanisms to be manufactured for the locking mechanism or a different printer housing (which means that the standard commercial printers being manufactured cannot be used for public places, and that different printers need to be manufactured for use in public places).
Thus, it would be beneficial to provide a way to detect theft of print substance that did not have these problems.